Internally-threaded, self-clinching type fasteners are well-known in the art. When installed, they provide materials such as sheet metal panels with a threaded structure to receive a screw so that elements can be secured to the panel. A typical self-clinching fastener of the standoff type which includes an elongate barrel is shown in FIGS. 3 and 4. The basic structures of this type of fasteners include a head, a self-clinch groove, a barrel, and an internal bore with threads. The fastener is installed by a press and anvil so that the groove receives the cold flow of metal from the sheet while the polygonal head is embedded into the sheet. These structures secure the fastener to the sheet rigidly, both axially and rotationally.
One effective means for producing a self-clinching fastener of the above-described type is by a progressive die forging process. This process utilizes sequential punch and die forging to create the head, the clinch groove, the barrel, and the internal bore of the fastener from a metal blank or slug. Such a formation process is described for example in U.S. Patent Application Serial No. 2002/0054806 entitled “Grooved Nut and Manufacturing Method Thereof” filed on Jan. 3, 2001 by Sakamura et al. and published on May 9, 2002. This document discloses the progressive punch and die tooling used in this process as exemplified by FIG. 3. As shown in this figure, a horizontally reciprocating ram holds a series of punches, each opposite a respective die providing a series of forging stations. The punches and dies progressively form the basic shape of the fastener from a blank of metal which is moved between stations after each stroke of the ram. The shearing action between the punch and die of the final station trims metal from around the edge of a temporarily formed circular head of the fastener as the blank is pushed through the die by the punch to create the final polygonal shape.
A problem exists with this manufacturing process, however, because the shearing process in the last station of the progressive forging leaves an undesirable upward-facing burr on the top side of the head of the fastener. Furthermore, there is another problem with this final head trimming station in that the scrap ring which results from cutting the material away from the periphery of the circular head to achieve the final polygonal shape often sticks to the face of the trim die, obstructing the continuous operation of the progressive forging process. There is therefore a need in the art to utilize a cold forging process to create a self-clinching fastener which does not have these deficiencies.